Civil NIIRS Reference Guide

Prepared By
the Imagery Resolution
Assessments and Reporting
Standards (IRARS) Committee

Civil NIIRS Reference Guide

1.0 Introduction

This document presents the Civil National Imagery Interpretability Rating Scale (NIIRS) and discusses its use. Image examples using the Civil NIIRS are displayed in Appendix I. Additional Civil NIIRS criteria are listed in Appendix II and a history of NIIRS appears in Appendix III.

Comments or requests for additional copies should be directed to Mr. Rich Murphy, Technical Director of IRARS, at 703-799-XXXX.

1.1 What is NIIRS?

The National Imagery Interpretability Rating Scale (NIIRS) is a task-based scale used for rating imagery acquired from various imaging systems. The NIIRS originated in the Intelligence Community and is the standard used by imagery analysts, collection managers, imagery scientists, and sensor designers. The imagery analysis tasks that comprise the NIIRS have, in the past, focused mainly on military equipment. This document provides a scale that is relevant to environmental and civil users and serves as a "stand-alone" reference.

The concept underlying the NIIRS is that imagery analysts should be able to perform more demanding interpretation tasks as the quality or interpretability ofthe imagery increases. The NIIRS consists of 10 graduated levels (O to 9), with several interpretation tasks or criteria forming each level. These criteria indicate the amount of information that can be extracted from an image at a given interpretability level. With a NIIRS 2 image, for example, analysts should lust be able to detect large buildings, while on NIIRS 6 imagery they should just be able to identify automobiles as sedans or station wagons.

1.2 Why NIIRS?

The NIIRS provides a common framework for discussing the interpretability, or information potential, of imagery. NIIRS, therefore, serves as a standardized measure of image interpretability for:

1.3 Civil NIIRS Criteria

The Imagery Resolution Assessment and Reporting Standards (IRARS) Committee is providing this reference guide in response to the rising importance of civil and environmental imagery applications of various imaging systems. The criteria presented here are divided into three categories based on the type of image exploitation task. The categories are:

These additional criteria expand the variety of NIIRS exploitation tasks, enabling analysts to find tasks that more closely resemble specific interests. Thus, the Civil NIIRS supplements the Visible NIIRS1 by expanding the number of criteria categories. In this sense, Civil NIIRS can be viewed as both a stand-alone scale and an expansion of the Visible NIIRS. See Table 1 for Civil NIIRS criteria.

1. The Visible NIIRS was developed by the Intelligence Community for rating panchromatic imagery. The criteria that form the Visible NIIRS address mainly military image interpretation tasks. A detailed discussion appears in Appendix III.


Civil NIIRS Reference Guide

Table 1. Civil NIIRS Criteria

Rating Level O
Interpretability of the imagery is precluded byobscuration, degradation, or very poor resolution.

Rating Level 1
Distinguish between major land use classes (e.g., urban, agricultural, forest, water, barren).
Detect a medium-sized port facility.
Distinguish between runways and taxiways at a large airfield.
Identify large area drainage patterns by type (e.g., dendritic, trellis, radial).

Rating Level 2
Identify large (i.e., greater than 160 acre) center-pivot irrigated fields during the growing season.
Detect large buildings (e.g., hospitals, factories).
Identify road patterns, like clover leafs, on major highway systems.
Detect ice-breaker tracks.
Detect the wake from a large (e.g., greater than 300') ship.

Rating Level 3
Detect large area (i.e., larger than 160 acres) contour plowing.
Detect individual houses in residential neighborhoods.
Detect trains or strings of standard rolling stock on railroad tracks (not individual cars).
Identify inland waterways navigable by barges.
Distinguish between natural forest stands and orchards.

Rating Level 4
Identify farm buildings as barns, silos, or residences.
Count unoccupied railroad tracks along right-of-way or in a railroad yard.
Detect basketball court, tennis court, volleyball court in urban areas.
Identify individual tracks, rail pairs, control towers, switching points in rail yards.
Detect jeep trails through grassland.

Rating Level 5
Identify Christmas tree plantations.
Identify individual rail cars by type (e.g., gondola, flat, box) and locomotives by type (e.g., steam, diesel).
Detect open bay doors of vehicle storage buildings.
Identify tents (larger than two person) at established recreational camping areas.
Distinguish between stands of coniferous and deciduous trees during leaf-off condition.
Detect large animals (e.g., elephants, rhinoceros, giraffes) in grasslands.

Rating Level 6
Detect narcotics intercropping based on texture.
Distinguish between row (e.g., corn, soybean) crops and small grain (e.g., wheat, oats) crops.
Identify automobiles as sedans or station wagons.
Identify individual telephone/electric poles in residential neighborhoods.
Detect foot trails through barren areas.

Rating Level 7
Identify individual mature cotton plants in a known cotton field.
Identify individual railroad ties.
Detect individual steps on a stairway.
Detect stumps and rocks in forest clearings and meadows.

Rating Level 8
Count individual baby pigs.
Identify a USGS benchmark set in a paved surface.
Identify grill detailing and/or the license plate on a passenger/truck type vehicle.
Identify individual pine seedlings.
Identify individual water lilies on a pond.
Identify windshield wipers on a vehicle.

Rating Level 9
Identify individual grain heads on small grain (e.g., wheat, oats, barley).
Identify individual barbs on a barbed wire fence.
Detect individual spikes in railroad ties.
Identify individual bunches of pine needles.
Identify an ear tag on large game animals (e.g., deer, elk, moose).


Civil NIIRS Reference Guide

1.4 Description of the NIIRS

Since the NIIRS was first released in the early 1970s, it has established its value to imagery analysts, imagery scientists, and collection and program managers. It serves as a standardized indicator of imagery usefulness for planning military missions, tasking various collection systems, evaluating system performance, and developing new systems. A history of the NIIRS and presentation of other scales (Visible NIIRS, Radar NIIRS, IR NIIRS) appears in Appendix III.

The Civil NIIRS consists of several criteria at each rating level. These criteria incorporate interpretation tasks familiar to experienced imagery analysts. All criteria within a single rating level can be achieved by imagery of approximately the same interpretability. The 10 rating levels that comprise the scale are equally spaced in interpretability.

To assign a NIIRS rating to an image, imagery analysts are asked to judge which tasks they can accomplish and which features they can see in the imagery. In making such judgments, the imagery analyst takes into account scene content and image acquisition conditions. Obviously, not every image contains the specific items mentioned in the criteria. When features referenced in the criteria are not present, the analyst must imagine these objects are present and make an educated guess as to which criteria can and cannot be accomplished on the image. In other words, the imagery analyst rates interpretability by judging what tasks could be accomplished or what features could be seen on an image of that aquality, as if the information needed to do the tasks or the features included in the scale were present in the image. In this way, the imagery analyst is in fact judging the information potential of the image, rather than making judgments about what was or was not actually imaged.

2.0 Assinging NIIRS Ratings

The NIIRS is intended to provide imagery analysts with uniform and systematic points of reference for judging relative image interpretability. To apply the NIIRS, the imagery analyst should:

To arrive at the most accurate NIIRS rathing, the imagery analyst should adhere to the following guidelines:


Civil NIIRS Reference Guide

2.1 Definitions

The terms detect, distinguish between, and identify are used extensively in the NIIRS criteria. Although there are several definitions of these terms currently in the image analysis community, their definition for NIIRS purposes is intended to be straightforward and uncomplicated. The definitions are:

3.0 Using the CIVIL NIIRS

The Civil NIIRS criteria are calibrated to the Visible NIIRS. Thus, an image that contains both cultural/natural features and military equipment can be rated using either the traditional Visible NIIRS or the Civil NIIRS presented here. The two approaches will yield the same NIIRS rating, on average2.

A major use for the Civil NIIRS will be to assist in tasking imaging systems and imagery collection management. Analysts assessing natural and environmental phenomena may not find relevant criteria in the Visible NIIRS to guide their tasking. The Civil NIIRS is more likely to represent tasks that will assist in articulating requirements in terms of NIIRS. This approach also applies to identifying historic archived imagery for environmental analysis.

2. Two analysts will occasionally assign different ratings to the same image because assigning a NIIRS rating to an image is a subjective process. The calibration of the Civil NIIRS ensures that ratings made with the Civil NIIRS and the Visible NIIRS will agree in most cases. To be precise, if a large number of images were rated using both scales, the mean difference between the two sets of ratings would not differ significantly from zero.


Civil NIIRS Reference Guide